New swamp cooler blowing slow

Hi everyone 1st post so i hope im doin it right.

Ok so here is the story

We bought our house in feb and discovered in june that the swamp cooler was wasted. So.....went to home depot and got a new one. Its a down draft 1800sq ft model and i put a 1/2 hp motor in it. Everything has been great up untill a week ago. Now the motor runs slow when the pump is on. Its weird though the way it works.... It will start fine in low cool and run at normal speed for maybe a minute and then instantly slow down. If i switch it to high cool after its already running slow it just vibrates and wont speed up. If i switch it to low or high vent it stays slow/vibrates for a minute or so and then picks up and runs normal and will do so indeffinately. If i come home and switch it to high or low vent it runs normal untill i switch it high or low cool. WTF!!!?? So ok.....i figured it must be the switch. Just replaced it and it still does all the same things. Now what? Should i look into my wiring? Or is my new-but-just-out-of-warranty motor no good? Any help would be greatly appreciated! Thank you!

P.s. My house is pretty old but i seem to have copper romex coming to the switch.....who knows whats in the attic.

New swamp cooler blowing slow

New swamp cooler blowing slow

That motor has no capacitor, it has a centrifigul switch with a start winding. You dont mention what size the cooler is but if it is the 6500 cfm model, you need to be running a 3/4 or 1 horsepower motor.
Cooler motors are not high quality anymore and I've had plenty of trouble with some newer ones, probably need to replace it.

I have two coolers on our house and one of them is only wired to run on low speed but when I turned it on this morning, it jumped to high! Go figure.

Also, when you install your new motor, make sure you adjust the pulley appropriately. If you have ductwork attached, it needs to be adjusted larger to make up for static loss. If it just dumps down into a common area, adjust the pulley out a few turns to avoid motor stalling. Best way to set it up, is to use a clamp on type meter to read what amps the motor is pulling. I dont understand the deal with the motor acting up when your pump is on, recheck your wiring at the switch and in the cooler but either way, your motor is too small for that cooler.

New swamp cooler blowing slow

I bought the biggest motor that this cooler was rated for. I had a thought today though.... What if my pump is going out and causing a large draw. Would that make sense?

Those pumps wont do that but It's possible that something is wrong with the pump.

If you want to make the cooler a little more modern, you can add a low voltage thermostat kit to it. It will pre wet the pads before starting the unit and it will also change speeds for you automatically as needed. The other nice thing about them is that you dont need so many high voltage wires between the cooler and wall switch, it uses a low voltage stat wire instead.

New swamp cooler blowing slow

It sounds like you are not getting enough power to the unit. Is the cooler on a dedicated breaker? when you flip the breaker off does it turn off anything else in the house? If it's not on a dedicated breaker then you need to call an electrician to install a dedicated breaker. If it is on a dedicated breaker I would assume it has something to do with the wiring. Either way an electician would be your best bet.